I'm sorry for the misunderstanding. I'd like to use OSM data to an app. The app isn't ready yet but I have inserted several roads and spots in a specific greek island (in OSM map) and I would like to ensure that noone will be able to change these in order to use them whole to my upcoming app. Thank you, I hope I'm clear now!

That is not how OSM works. Everything is editable by everybody and in general that is a good thing (forgetting about the occasional vandal), because that means that other contributors will build on your edits, will improve them, just as you can with other contributors edits.

If you want to have "private" data you are going to have to store it in a private server (which btw isn't so difficult, but does require a non-neligble amount of hardware).

Also, if your app gets its OSM data from a source you control (for example by importing an extract of Greece at a time of your choosing), you can spot-check the imported data before making it available to the app.